Cache the output of the command `mix credo info` until the `credo.exs`

[pantajoe]

Right, now in the Linter class, the command mix credo info (which is used to determine whether an actively edited file should be linted with credo) is executed on every lint request.

That's very inefficient and therefore should be stored in the a workspace project's configuration and only re-fetched when the credo configuration changes.